1. Field of Invention
The inventive concepts disclosed and claimed herein relate to a particle obtained by treating titanium dioxide with a polysiloxane. Blends of these particles with organic polymers are disclosed.
2. Background of the Invention
Titanium dioxide has found widespread use. Typically it is used in another matrix to impart certain properties. For example, it is widely used as a white pigment for paints and polymers. Other applications use small particle titanium dioxide which has different optical properties. For these and other applications, it is critical to have good dispersion of the titanium dioxide. Dispersing agents are often added to the titanium dioxide. Selection of the dispersing agent is often a compromise between effectiveness, cost, compatibility with other additives in the matrix, and performance properties in the matrix. For this reason, much work has been done to improve the dispersion of titanium dioxide in various matrices.
A variety of treatments has been studied. U.S. Pat. No. 6,646,037 treats the titanium dioxide with alkyl sulfonic acid salts and U.S. Pat. No. 6,765,041 discloses treatment with alkyl phosphate esters. Organosilicon compounds have been used. For instance, U.S. Pat. No. 4,061,503 discloses the treatment of particulate titanium dioxide with a polyether-substituted silicon compound for improving the dispersibility of titanium dioxide in pigmented and/or filled paints and plastics, and reinforced plastic composite compositions.
U.S. Pat. No. 4,810,305 discloses an organopolysiloxane with improved dispersibility. The polysiloxane is a hydrosiloxane such as polymethylhydrosiloxane. U.S. Pat. Nos. 5,607,994, 5,631,310, 5,889,090, and 5,959,004 disclose the use of a mixture of a hydrolyzable silane such as butyltrimethoxysilane and a polysiloxane such as polydimethylsiloxane. U.S. Pat. No. 5,932,757 describes a mixture of oligomers of alkylalkoxysilanes.
U.S. Pat. No. 6,620,234 discloses mixing a reactive chlorosilane such as hexyl trichlorosilane with titanium dioxide in an aqueous media to form coated titanium dioxide. The byproduct hydrochloric acid is neutralized and removed as a salt.
While there have been much research regarding the coating of titanium dioxide with silanes and siloxanes, further improvements are needed. To date, treatment techniques are often a compromise between processability and final properties. Many silicon-containing compounds are not sufficiently reactive with titanium dioxide to provide effective coatings. Other silicon-containing compounds are either volatile or produce volatile side products. In an effort to improve reactivity, functional groups such as alkoxy groups have been used, but the alcohol generated as a byproduct can cause environmental issues during pigment production. Use of halosilanes in aqueous media can solve this problem, but it is a more complicated process and adds to the cost. Despite the significant research done in this area, there is a need for further improvements.